For better resolution in lithographic processes, an antireflective coating (ARC) material may be used to minimize the reflectivity between an imaging layer, such as a photosensitive resist layer, and a substrate. However, because the resist layer often has a composition similar that of the ARC material, the ARC material may provide poor etch selectivity relative to the imaging layer. Accordingly, since large portions of the imaging layer may be removed during etching of the ARC material after patterning, additional patterning may be required in a subsequent etching step.
However, in some lithographic imaging processes, the resist material may not provide sufficient etch resistance to effectively transfer the desired pattern to a layer underlying the resist material. In actual applications, a so-called hardmask for a resist underlayer film may be applied as an intermediate layer between a patterned resist and the substrate to be patterned. For example, when an ultrathin-film resist material is used, the substrate to be etched is thick, a substantial etching depth is required, and/or the use of a particular etchant is required for a specific substrate, a hardmask for the resist underlayer may be desirable. The hardmask for a resist underlayer film may receive the pattern from the patterned resist layer and transfer the pattern to the substrate. The hardmask for a resist underlayer film should be able to withstand the etching processes needed to transfer the pattern to the underlying material.
For example, when a substrate, such as silicon, is processed, a resist pattern may be used as a mask. At this time, the resist may be micropatterned but with a decreased thickness. Thus, since the masking properties of the resist may be insufficient, processing of the substrate may result in damage to the substrate. Therefore, a process may be employed whereby a resist pattern is first transferred to an underlayer film (e.g., a hardmask) for the processing of the substrate, followed by dry etching of the substrate using the underlayer film as a mask. The underlayer film for the processing of the substrate refers to a film that may be formed under an antireflective film and may also function as an antireflective layer. In this process, the etching rate of the resist may be similar to that of the underlayer film for the processing of the substrate. Thus, it may be necessary to form a hardmask, which may also be antireflective, for processing the underlayer film between the resist and the underlayer film. As a consequence, a multilayer film consisting of the underlayer film for the processing of the substrate, the hardmask for processing the underlayer film and the resist may be formed on the substrate.
Various hardmask materials have been investigated. For example, Japanese Unexamined Patent Publication No. 2000-0077018 describes the use of polycondensation products of silane compounds of the general formula of RaSi(OR)4-a in resist underlayer films. One problem associated with the use of such polycondensation products is that unreacted starting material and/or low molecular weight by-products obtained during the polycondensation may undesirably interact with a photoresist layer on the hardmask layer and result in deterioration of pattern characteristics.
Thus, it would be desirable to identify hardmask compositions and methods of using the same that minimize unreacted starting material or low-molecular weight byproducts in formed hardmask layers.